![]() Because only small (expensive) quantities of powder are available during early dosage-form design and because the synthetic process may not be finalized, having a simple material-sparing screening tool that can rapidly evaluate the powder flow of these samples is attractive (3). Amidon and Houghton remark that useful powder-flow evaluation tools should be reproducible, sensitive, yield meaningful results, and require small amounts of material (3). The quantification of powder-flow properties with a small quantity of material (<20 g) is essential for material sparing and cost-saving predictive assessments. The absolute size and distribution of particles in a powder sample, therefore, collectively contribute to the sample's bulk powder-flow behavior. In addition, a broad particle-size distribution (PSD) with both large and small particles enables more efficient particle packing, which leads to an interlocking effect as the small particles fill in the gaps between the contact surfaces of larger particles. This is because gravity forces significantly exceed interparticle forces such as those caused by electrostatic or van der Waals interactions for particles in this size range. ![]() Small particles (100 μm) tend to roll or slide over one another when a shear stress is present and, thus, exhibit superior bulk flow properties compared with small particles. It is well established that particle size (mean and distribution) is one of the most significant factors that affects the flow behavior of powders (1, 2). Free-flowing powders are desirable to enable robust powder processing operations such as bin filling, hopper discharge, and capsule and die filling. These descriptions of materials and methods address the preparation of samples and the fingerprint development processes with powder suspension and VMD.Pharmaceutical powders can be very different in their particle chemistry, morphology, and size, which can significantly affect their bulk-flow properties. These included black bin bags, orange carrier bags, clear sandwich bags, and black cowlings. Various types of substrates representative of common nonporous materials were examined. In addition, VMD developed a larger percentage of potentially identifiable prints (grades three and four). VMD also proved to be a more sensitive technique for clear sandwich bags across all ages, recovering all but 2 of the 280 half prints that were deposited. VMD proved to be more effective in developing a larger number of prints that contained more than 1/3 ridge detail (grades three and four). Both techniques, with the exception of powder suspension at 14 days, developed a large number of visible prints on orange plastic bags, with VMD recovering slightly more visible prints across all print ages compared with Wetwop. ![]() ![]() The prints developed with VMD were not as easy to see as those developed by Wetwop, and various lighting techniques were necessary to view the ridge detail that was present. ![]() The performance of the white-powder suspension was particularly superior to VMD for prints that had aged 14 days. The value of using the powder suspension technique was particularly relevant for cowlings, where it significantly outperformed VMD. The study found that the powder-suspension technique was more successful in developing more potentially identifiable prints than the VMD technique for deposition on black bin bags and cowlings (removable engine coverings). ![]()
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